1. Field of the Invention
The present invention relates generally to the field of electromechanical translators and particularly to those translators which are capable of motion in incremental steps, which are often referred to herein as step and repeat motors.
2. Description of the Prior Art
The fundamental topology of a typical prior art step and repeat motor apparatus is schematically illustrated in FIG. 1 of the present application. The basic step and repeat motor apparatus of FIG. 1 is generally indicated by the numeral 10. The apparatus 10 includes a base 12 schematically illustrated in FIG. 1 as the various grounded or fixed points 12. The apparatus 10 includes two active clamping elements 14 and 16, one translator drive element 18, and an output member 20. The translator drive element 18 is in line with and constitutes a middle portion of the output member 20. The translator drive element 18 is an active element which may also be referred to as an extending actuator 18 can expand or contract in the direction 22 of motion of the output member 20, which may also be referred to as a motor output shaft 20, according to the voltage or other signal applied to the translator drive element 18, so that it can linearly move the output member 20 that is attached to the ends of the translator drive element 18. The two clamping elements 14 and 16 are placed perpendicularly to the direction 22 of the translator drive element 18 and the moveable output member 20. The clamping elements 14 and 16 act along their extension/contraction direction 24 and have the role of clamping alternately on either one or the other end of the output member 20 by applying pressure to top pressure plates 26 and 28. By properly sequencing the action of the electroactive material actuators which are part of the clamping elements 14 and 16 and the translator drive element 18, the body formed by the translator drive element 18 and the output member ends 20 can be moved linearly in either direction 22.
As will be understood by those skilled in the art, a step and repeat motor moves the output member 20 in a continuous sequence of small incremental steps to create a continuous larger movement of the output member 20. A typical three stage operation sequence comprising one small step of the apparatus 10 from left to right as seen in FIG. 1 proceeds as follows. In the initial step sequence the clamping element 14, which may be referred to as a trailing clamping element, is extended so as to clamp the operating element 20 at the point below the clamping element 14. The clamping element 16, which may be referred to as a leading clamping element, is relaxed or contracted so as to release the portion of the output member 20 located therebelow. The translator drive element 18 is expanded which will cause one small step of movement from left to right of that portion of the output member 20 located below the leading clamping element 16.
Next, the leading clamping element 16 is expanded to clamp the operating element 20 therebelow, the trailing clamping element 14 is contracted to release the operating element 20 located therebelow, and the translator drive element 22 is contracted which causes that portion of the operating element 20 below the trailing clamping element 14 to move one small step from left to right. Thus the entire operating element 20 has been translated from left to right through one small step of motion, which for example may be typically in the range of from 1.0 to 100 μm. The process is now repeated many times in a very rapid fashion to move the operating element from left to right the required distance. Reversing the sequence can, of course, move the operating element from right to left.
Examples of Various Step and Repeat Motor Topologies Known in the Prior Art
U.S. Pat. No. 3,902,084 to May, Jr. discloses a step and repeat translating device moveable over long distances with fine resolution using damper and driver elements to advance a shaft.
U.S. Pat. No. 3,902,085 to Bizzigotti discloses a step and repeat translating device that is made up of a piezoelectric driver with three different sections surrounding a central shaft. The three sections of the driver can move relatively to each other and engage with the shaft producing a linear motion of the shaft.
U.S. Pat. No. 4,570,096 to Hara et al. discloses an electromechanical translation device having a moveable shaft, several electrostrictive layers disposed longitudinally along the shaft and an external housing.
U.S. Pat. No. 5,027,027 to Orbach et al. discloses an electromechanical translation apparatus having a driver that is fixed with respect to a base, a forward element, a rear element and a central driven element. The active center element can vary the distance between the forward and rear elements, which can selectively clamp/unclamp the central driven element and thus imparting a linear motion to the said driven element.
U.S. Pat. No. 5,319,257 to McIntyre discloses a uni-axial constant velocity microactuator that is designed to operate in ultra-high vacuum environment. The mechanism has a flexible coupling with a bore therethrough and two end clamp/pusher assemblies that are piezoelectrically actuated and that engage and linearly move a shaft that passes through the hole of the flexible coupling.
U.S. Pat. No. 5,332,942 to Rennex discloses a piezoelectric motor design that orients the clamping drivers parallel to the drive direction for the purpose of miniaturization.
U.S. Pat. No. 6,380,661 to Henderson et al. discloses a linear bi-directional motor driven by induced strain actuators. Using MEMS technology, a frame can be machined to incorporate micro-ridges on the base of the motor for the auxiliary actuators to alternately engage.
U.S. Pat. No. 6,800,984 to Marth discloses a piezo linear drive that uses one stack part configured as a longitudinal clamping actuator, and a second stack in series configured as a shearing actuator to control motion of a moving member.
Piezoelectric/Electroactive Motors Producing Linear Motion
U.S. Pat. No. 4,219,755 to O'Neill et al. discloses an electromotive actuator having a hollow cylinder with an inner electroexpansive body having attached one slotted metal cup at each end with an expanding disk within it that can clamp/unclamp the respective disk on the hollow cylinder. By conveniently sequencing the deformation of the central body and of the two disks, the assembly generates a bi-directional linear motion that can be transmitted to an external rod.
U.S. Pat. No. 4,736,131 to Fujimoto discloses a linear motor that includes a pair of amplified piezoelectric actuators. A second piezoelectric actuator connects the pair of actuators and translates the levers of the pair of piezoelectric actuators perpendicular to the direction of actuation of the levers.
U.S. Pat. No. 4,777,398 to Shibuya et al. discloses a linear piezoelectric motor that has a shaft and a shaft housing whereby the shaft can steppingly slide into its housing by means of actuation received from an amplified piezoelectric-driven mechanism.
U.S. Pat. No. 4,874,979 to Rapp discloses another electromechanical translation apparatus that can be used for positioning in a scanning tunneling microscope. The mechanism is formed of a moving shaft that is surrounded by a piezoelectric driver in the form of a sleeve and which has an extension element and two clamping elements at its opposite ends.
U.S. Pat. No. 5,640,063 to Zumeris et al. discloses a linear stepping motor having several pairs of piezoelectric motors that produce a sinusoidal square wave that results in a linear motion of the moveable part.
U.S. Pat. No. 5,786,654 to Yoshida et al. discloses a moveable stage that utilizes an electromechanical transducer. A piezoelectric actuator is used as a driver to linearly displace a moveable member that is frictionally coupled with the driver.
U.S. Pat. No. 6,239,533 to Burov et al. discloses a piezoelectric step motor having a moveable part that resides inside of a fixed part and is frictionally displaced in a linear fashion by several contact parts that are acted upon by several piezoelectric units acting in unison.
U.S. Pat. No. 6,337,532 to Johansson et al. discloses an electromechanical actuator having a plurality of drive elements that produce a walking motion of the arrangement relative to a fixed body. Each drive element is actuated in a cycle comprising gripping, moving the mobile body, releasing it and returning to the initial position.
Piezoelectric/Electroactive Motors Producing Linear Motion Using Various Preload Methods
The following patents involve the use of a spring or mechanically applied force through the clamping element in order to provide a preload to some portion of the motor.
U.S. Pat. No. 3,840,759 to Guntersdorfer et al. discloses a piezoelectric linear motor having a plurality of strips that are mechanically connected in parallel and packed between a fixed part and a moveable part. Piezoelectric excitation of the flexible strips generates bending of the said strips that translates into linear motion of the moveable part.
U.S. Pat. No. 5,424,597 to Gloss et al. discloses a piezo device with two piezo translators that are brought into connection with the driven elements by means of spring elements that engage and disengage independent of each other.
U.S. Pat. No. 5,751,090 to Henderson discloses a peristaltic driver using stepping action of piezoelectric actuators. Referring to FIG. 4 of Henderson its peristaltic driver is located between two rails 50 and 52, one of which may move relative to the other. A compressive preload is provided by spring 58. The Henderson device does not provide any structure to prevent twisting of the moveable rail 50, and due to the topology of the peristaltic driver used in Henderson with a multitude of clamping elements and translator elements the peristaltic drive element itself appears to hold the two rails 50 and 52 in position relative to each other with the peristaltic driver clamped therebetween.
U.S. Pat. No. 6,313,566 to Cunningham et al. discloses a piezoelectric motor that is made up of a motor body, a compliant layer, a specified number of piezoelectrically-actuated legs and a substrate. By actuating the piezoelectric legs in a predetermined fashion their corresponding deformation and energy are transmitted to the compliant layer. The energy stored in the compliant layer may be released, causing the motor to advance along the substrate.
Piezoelectric Motors being Driven Using Resonant Frequencies
U.S. Pat. No. 6,765,335 to Wischnewskiy discloses a piezoelectric adjusting element in the form of a piezoelectric oscillator and groups of electrodes sending longitudinal acoustic waves in the direction of an oscillator resonant length and oscillator resonant height.
U.S. Pat. No. 6,806,620 to Wischnewskiy discloses a piezoelectric drive that excites the driven element by use of longitudinal and flexural acoustic waves.